JP-2010-71348A discloses a technique for attaching a control component unit (an electronic circuit device 20 described therein) to an outer surface of a transmission casing of a vehicle. Generally, such a control component unit is attached to an upper surface of the transmission casing such that the control component unit has a substantially horizontally extending posture. JP-2010-223313A and JP-2015-90203A disclose techniques for attaching a noise insulating covering to an outer surface of a transmission casing of a vehicle.